Convert List to String

List of String:

String.join(",", yourListString);

List of Objetcs:

String content = yourListObjs.stream()
        .map(obj -> obj.toString())
        .collect(Collectors.joining(System.lineSeparator()));

Sort List of Objects by Property

yourList.sort(Comparator.comparing(obj -> obj.getYourProperty));

Sort List of String:

list.sort(String::compareToIgnoreCase);